1. Field of the Invention
The present invention generally relates to optical apparatus and, more particularly, is directed to an optical apparatus for use with a virtual image display which magnifies and displays an image as a virtual image by a lens and so on.
2. Description of the Prior Art
In recent years, a stereoscopic (or three-dimensional effect) television using a lens and a liquid crystal panel or the like has been proposed (see Japanese Patent Laid-Open Gazette No. 59117889). A fundamental principle of such previously-proposed liquid crystal stereoscopic television will be described with reference to FIG. 1.
Referring to FIG. 1, there is shown a convex lens 6 which is composed of a plurality of lenses in actual practice, and a transmission-type liquid crystal display 7 is supported in front of the convex lens 6 by a supporting device 8 together with the convex lens 6 to thereby display a video image on a display screen 9 of the transmission-type liquid crystal display 7. The transmission-type liquid crystal display 7 is disposed within a focal length f of the convex lens 6. Also, an eye 5 is distant from the convex lens 6 by a distance of 1 to 3 cm in the opposite side of the transmission-type liquid crystal display 7.
With the above arrangement, the transmission-type liquid crystal display 7 is disposed within the focal length f of the convex lens 6 so that, when the viewer views a video image on the display screen 9 of the transmission-type liquid crystal display 7 from the eye 5 side through the convex lens 6 by natural light or guided light 10, the viewer can watch a virtual image 4 in the enlarged form at the position distant from the actual position in which the video image is displayed on the display screen 9.
FIG. 2 is a plan view of the optical system of FIG. 1. As shown in FIG. 2, left and right convex lenses 6L and 6R for magnification are respectively disposed between left and right eyes 5L, 5R and left and right transmission-type liquid crystal displays 7L, 7R, whereby video images displayed on the left and right transmission-type liquid crystal displays 7L, 7R are magnified and stereoscopic virtual images are displayed on left and right virtual image planes 4L, 4R, respectively.
In the conventional virtual image display device of lens magnification type shown in FIGS. 1 and 2, the left and right convex lenses 6L, 6R are located very close to the left and right eyes 5L, 5R. Thus, when the viewer wears the virtual image display of this arrangement, the viewer cannot see the view of the surroundings without taking off such virtual image display device, which is very dangerous.
Further, there is a conflict between inclinations (congestion angles) of the left and right eyes 5L, 5R and the focusing adjustment of crystalline lenses used in the display. More specifically, video images on the left and right virtual image planes 4L, 4R viewed by the left and right eyes 5L, 5R shown in FIG. 2 must coincide with each other. However, a distance l.sub.1 between the human left and right eyes 5L and 5R is not always the same so that a length l.sub.2 between the left and right convex lenses 6L and 6R must be moved or adjusted. If the length l.sub.2 is changed, the positions of video images displayed on the left and right virtual image planes 4L, 4R will be displaced. FIG. 3 is a schematic diagram used to explain an example in which the video images displayed on the left and right virtual image planes 4L, 4R are displaced in position. In FIG. 3, the virtual image plane 4L is for the left eye and the virtual image plane 4R is for the right eye. A predetermined point A.sub.L on the virtual image plane 4L viewed by the left eye 5L and a predetermined point A.sub.R on the virtual image plane 4R viewed by the right eye 5R should be displayed at the same position.
When the viewer watches such an object by this virtual display, inclinations of left and right eyes become .phi..sub.1 and .phi..sub.2, which means that the viewer watches a hypothetical point A on a plane S1. On the other hand, the left and right eyes 5L, 5R are focused on the points A.sub.R, A.sub.L on the virtual image planes 4R, 4L so that the focused states of crystalline lenses and the inclination angles of both eyes are not coincident, thereby viewer's eyes being fatigued.